The present and proposed industrial development associated with the Athabasca Oil Sands has resulted in a need to evaluate the Athabasca River transport and assimilation of contaminants and water occurring substances. Since the beginning of AOSERP in April 1975, water quality and quantity data have been collected to provide a general baseline of information. Preliminary studies of the Athabasca River Basin indicate that a mass balance approach may be used to model the chemistry of the Athabasca River. The base model developed provides a reasonable analysis of dissolved sodium, dissolved chloride, total alkalinity, and total hardness between Fort McMurray and the Embarras Airport. It appears possible now to investigate transformations, impacts, and assimilation of non-conservative substances in the Athabasca River utilizing the mass balance concept developed for conservative substances in the study. Once the composite model is calibrated and tested, it would predict mass loading or concentration of a parameter at any point along the study area for different future development scenarios. The resulting evaluations of these development scenarios will allow comprehensive management planning to be completed for the Athabasca watershed.